1. Field of the Invention
The present invention relates to a vacuum generating unit, which supplies a negative pressure to a working device such as a suction pad or the like, and more specifically, to a vacuum generating unit having a solenoid valve section therein capable of switching between supplying and cutting off supply of the negative pressure.
2. Description of the Related Art
Conventionally, a vacuum generating unit has been known, which is used, for example, as a workpiece transport mechanism or as a positioning mechanism. In such a vacuum generating unit, a suction mechanism such as a suction pad or the like is connected to the unit main body, whereby under the action of a negative pressure which is supplied from the unit main body, a workpiece can be attracted under suction by means of the suction mechanism. In addition, transportation of the workpiece is carried out, in which the workpiece is displaced while maintaining the suction state, and the workpiece is released at a predetermined location by canceling the suction state.
For example, in Japanese Laid-Open Patent Publication No. 2003-042134, a vacuum generating unit is disclosed in which a vacuum pump is utilized as a vacuum generating mechanism. In this vacuum generating unit, a vacuum generating valve is connected to the vacuum pump, and a vacuum-breaking valve is connected to a compressed air source, whereby airflows therefrom are controlled respectively. In addition, when the vacuum generating valve is switched from an OFF state to an ON state, a vacuum is generated in a vacuum port, while communication with atmosphere is cut off under a switching operation of an atmospheric pressure supply valve.
Further, the vacuum-generating device disclosed in Japanese Laid-Open Patent Publication No. 2002-224984 is equipped with a controller for ON/OFF control of the supply state of compressed air supplied from a supply port, and a vacuum generating section, which during an ON state, generates a vacuum by injecting, through a nozzle, the compressed air fed into a cylinder, passing the compressed air through a diffuser spool, and then discharging the compressed air from an exhaust port. Moreover, the diffuser spool is movably disposed in an axial direction inside the cylinder, such that, in the case that the supply of compressed air is turned OFF, the diffuser spool is moved, whereby the vacuum is capable of being broken via the exhaust port, an auxiliary pathway, and the diffuser spool.
However, in the conventional techniques according to Japanese Laid-Open Patent Publication No. 2003-042134 and Japanese Laid-Open Patent Publication No. 2002-224984, in order to quickly release the held state of the workpiece by the vacuum pressure, a vacuum breakage valve for breaking the vacuum and an atmospheric pressure supply valve are provided separately, and together therewith, a structure is provided in which the atmospheric pressure supply valve is normally in an open state, and compressed air, which is supplied to the diffuser for generating the vacuum pressure, is utilized for switching to a valve closed state. Owing thereto, for example, in the case that the vacuum generating unit is utilized in a pump system or the like, in which vacuum pressure is supplied from the exterior, because the diffuser is not provided, the atmospheric pressure supply valve cannot be switched to a valve closed state.
Further, in this type of vacuum generating unit, because attraction under suction of the workpiece is performed, whereupon the supplied amount of compressed air is reduced when the workpiece is in a held state, communication with the atmosphere results through the atmospheric pressure supply valve, which is in a valve open state, and thus holding of the workpiece cannot be performed.